Flexible stretch stent-graft

ABSTRACT

A stent device ( 10 ) comprises a first graft member ( 20 ), a second graft member and a stent frame ( 12 ) defining a central axis. The frame has an abluminal surface engaged with the first graft member and a luminal surface engaged with the second graft member such that the first graft member and the second graft member encapsulates the stent frame along the length of the central axis. The stent frame includes a configuration where the stent frame is disposed on a curvature such that the abluminal surface has a radius of curvature of approximately 20 millimeters about a center of the curvature and the luminal surface defines a substantially constant effective cross-sectional area at any portion generally transverse to the central axis of the stent frame disposed about the curvature.

BACKGROUND OF THE INVENTION

The present invention relates generally to the field of medical devices,and more particularly, to the stent grafts and their method of making.

Stents and similar endoluminal devices are currently used by medicalpractitioners to treat tubular body vessels or ducts that become sonarrowed (stenosed) that flow of blood or other biological fluids isrestricted. Such narrowing (stenosis) occurs, for example, as a resultof the disease process known as arteriosclerosis. While stents are mostoften used to “prop open” blood vessels, they can also be used toreinforce collapsed or narrowed tubular structures in the respiratorysystem, the reproductive system, bile or liver ducts or any othertubular body structure. However, stents are generally mesh-like so thatendothelial and other tissues can grow through the openings resulting inrestenosis of the vessel.

Apart from use of stents within the circulatory system, stents haveproven to be useful in dealing with various types of liver disease inwhich the main bile duct becomes scarred or otherwise blocked byneoplastic growths, etc. Such blockage prevents or retards flow of bileinto the intestine and can result in serious liver damage. Because theliver is responsible for removing toxins from the blood stream, is theprimary site for the breakdown of circulating blood cells and is alsothe source of vital blood clotting factors, blockage of the bile ductcan lead to fatal complications. A popular type of stent for use in thebiliary duct has been one formed from a shape memory alloy (e.g.,nitinol) partially because such stents can be reduced to a very lowprofile and remain flexible for insertion through the sharp bend of thebile duct while being, self-expandable and capable of exerting aconstant radial force to the duct wall. Polytetrafluoroethylene (PTFE)has proven unusually advantageous as a material from which to fabricateblood vessel grafts or prostheses, tubular structures that can be usedto replace damaged or diseased vessels. This is partially because PTFEis extremely biocompatible causing little or no immunogenic reactionwhen placed within the human body. This is also because in its preferredform, expanded PTFE (ePTFE), the material is light and porous and isreadily colonized by living cells so that it becomes a permanent part ofthe body. The process of making ePTFE of vascular graft grade is wellknown to one of ordinary skill in the art. Suffice it to say that thecritical step in this process is the expansion of PTFE into ePTFE. Thisexpansion represents a controlled longitudinal stretching in which thePTFE is stretched to several hundred percent of its original length.

Cellular infiltration through stents can be prevented by enclosing thestents with ePTFE. Early attempts to produce a stent covered by ePTFEfocused around use of adhesives or physical attachment such as suturing.However, such methods are far from ideal and suturing, in particular, isvery labor intensive. More recently methods have been developed forencapsulating a stent between two tubular ePTFE members whereby theePTFE of one-member touches and bonds with the ePTFE of the other memberthrough the mesh opening in the stent. However, such a monolithicallyencapsulated stent may tend to be rather inflexible. Moreover, evencovered stents that include slit cut and bridge connection designedgraft coverings tend to be inflexible because the covering graftmaterial is unable to expand lengthwise with the underlying stent frame.

Other solutions to provide a more flexible stent graft include a stentgraft device described in U.S. Pat. No. 6,579,314 which is incorporatedherein in its entirety by reference thereto and attached hereto asExhibit A. U.S. Pat. No. 6,579,314 describes a flexible stent graft thatuses a partially encapsulated stent having areas covered by only asingle layer of ePTFE in order to provide flexibility to the stent graftdevice. Another partially encapsulated stent is shown and described inU.S. Pat. No. 6,558,414 which is also incorporated herein in itsentirety by reference thereto and attached hereto as Exhibit B.

Other solutions provide for making a self-expanding stent longitudinallyexpandable. For example, U.S. Pat. No. 5,899,935 includes a method ofmanufacturing a stent in which the stent is stretched longitudinally toreduce its outer diameter and coated in a material to freeze thestretched configuration. In the description of use, the coating isdisintegrated to permit the stent to expand.

SUMMARY OF THE INVENTION

In one preferred embodiment of a stent graft, the stent graft isconfigured to prevent cellular infiltration and maintain its flexibilityto ensure ease of insertion and deployment of the stent graft byproviding the ability to accommodate extreme anatomical curves. Thestent graft device preferably includes a first graft member, a secondgraft member and a stent frame defining a central axis. The frame has anabluminal surface engaged with the first graft member and a luminalsurface engaged with the second graft member such that the first graftmember and the second graft member encapsulate the stent frame along thelength of the central axis. The stent frame further preferably includesa configuration where the stent frame is disposed about a center ofcurvature such that the abluminal surface has a radius of curvature ofapproximately 20 millimeters from the center of curvature and theluminal surface defines a substantially constant effectivecross-sectional area at any portion generally transverse to the centralaxis of the stent frame. Moreover, the stent frame further preferablyincludes a substantially straight portion continuous with the curvaturewhich defines an effective cross-sectional area substantially equal toan effective cross-sectional area proximate the curvature.

In another aspect of the preferred stent graft device, the curvature ofthe stent frame includes a gap proximate the apex of the curvature, thegap having a gap length, the first graft member having an expansionportion configured to span the gap, the expansion portion defining aradius of curvature substantially equal to about 20 millimeters. Theradius of curvature can further range from about 30 millimeters to about10 millimeters.

In another preferred embodiment, the stent device includes a stent framehaving a central axis, a luminal surface, and an abluminal surface. Thestent frame has at least one gap along the abluminal surface providingcommunication between the abluminal and luminal surfaces and furtherdefining a gap length. A generally tubular graft member is contiguouswith at least one of the luminal and abluminal surfaces of the stentframe. The graft member preferably includes an expansion portion to spanthe at least one gap. The expansion portion has a length greater thanthe gap length and which is preferably defined by the stent frame havinga radius of curvature of about 20 mm.

In yet another embodiment, the stent device includes a stent framehaving a first end and a second end defining a central axistherebetween. A tubular graft member is preferably concentrically boundwith the stent frame, and the graft member includes at least oneundulation between the first and second ends, the tubular graft memberbeing configured to extend along the central axis. Preferably, the stentframe has first and second states, wherein in the first state the stentframe is substantially straight such that the at least one undulation isdisposed proximate a gap in the stent frame and in the second state thestent frame defines a radius of curvature expanding the gap so as toeliminate the undulation.

According to a preferred method of making a stent-graft device, themethod, at least, can be achieved by tensioning a stent frame having anabluminal surface and a luminal surface to alter an initial aspect ratioof the stent frame and define a second aspect ratio. In addition, thepreferred method further includes coupling a tubular graft member to thestent frame, and relaxing the stent frame so as to contract the graftmember along the central axis. The method may include positioning thetubular graft member coaxially inside the stent and may include couplingthe tubular graft member to the abluminal surface. The method furtherpreferably includes disposing the first tubular graft member over amandrel and securing a first and second end of the first tubular graftmember about the mandrel. Tensioning the stent frame provides axiallyelongating the frame such that the frame is preferably elongated byabout fifteen to twenty percent (15%-20%) of its original length.Relaxing the stent frame contracts the stent graft device to a lengththat is preferably about one hundred ten percent to about one hundredfifteen percent (110%-115%) of the original stent frame length. Morepreferably, relaxing the stent frame provides the stent graft devicewith an expansion length that is about five to ten percent (5%-7%) thecontracted length of the stent graft device.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated herein and constitutepart of this specification, illustrate exemplary embodiments of theinvention, and together, with the general description given above andthe detailed description given below, serve to explain the features ofthe invention. It should be understood that the preferred embodimentsare not the invention but are some examples of the invention as providedby the appended claims.

FIG. 1 illustrates a preferred stent graft device.

FIG. 2. illustrates the device of FIG. 1 in a bent configuration,

FIGS. 2A-2C schematically illustrate a test protocol for kinking.

FIG. 2D is a cross-sectional view of the device of FIG. 2 through theline IID-IID

FIG. 3 is an illustrative embodiment of a stent frame for use in thepreferred stent graft device.

FIG. 4A is a detail of a schematic view of the stent frame in the deviceof FIG. 2.

FIG. 4B is another detail of the of the stent frame in the device ofFIG. 2.

FIG. 5A is a cross-sectional view of another preferred stent graftdevice.

FIG. 5B is a detailed cross-section view of another preferred stentgraft device.

FIG. 6 is an illustrative flow chart of a preferred method for forming astent graft device.

FIG. 7 is a cross sectional view of another preferred stent graftdevice.

FIG. 8 A is a detail of a schematic view of the stent frame in thedevice of FIG. 7.

FIG. 8B is another detail of the stent frame in the device of FIG. 7.

FIG. 9 is an illustrative flow chart of another method for forming astent graft.

DETAILED DESCRIPTION

A preferred stent graft device 10, as illustrated in FIG. 1 includes asubstantially tubular and elongated body 12 having opposing first andsecond ends 14, 16 spaced apart along a central axis A-A encapsulated ina sleeve of graft material 20. The body 12 includes a central passagewayor interior chamber 18 dimensioned and configured for the passagetherethrough of biological fluids such as, for example, blood. Thetubular body 12 and the interior passageway 18 are preferably circularcylindrical although other cross-sectional geometries are possible, suchas rectangular, oval, multi-lobed or polygonal, provided the bodyincludes the interior passageway 18 sufficiently dimensioned forcarrying the blood or other biological fluid. The tubular body 12 ispreferably configured to articulate flex and/or bend in order to, forexample, follow anatomical curves encountered during deployment andimplantation. In a curved configuration, the tubular body 12 of definesa radius of curvature R from a center of curvature off the tubular body,as illustrated in FIG. 2, to define an outer curved surface 24 and aninner curved surface 26. The radius of curvature R for the body 12 canrange from an infinite radius or a substantially straight configurationdown to a radius of about 20 millimeters which corresponds substantiallyto the most severe anatomical curvature likely to be encountered ortraversed in a body. The radius curvature at about 20 millimeters, inthe most severe anatomical curvature configuration for the body 12, canmore specifically range from about 30 millimeters to about 10millimeters.

More preferably, the tubular body 12 can articulate, flex and/or bendabout the radius of curvature R of about 20 millimeters with a high kinkresistance. As noted above, the interior passageway 18 defines a chamberthrough which biological fluids pass, preferably at a desired flow rate.Accordingly, the interior passageway 18 of the stent graft device 10defines an effective cross-sectional area through which such biologicalfluids can pass. The effective cross-sectional area is preferably at itsmaximum when the stent graft device 10 is in a substantially straightconfiguration. “Kink resistance” is preferably defined as maintaining asubstantially constant effective cross-sectional area for the stentgraft device 10 over the range of possible curvatures as the stent graftdevice 10 is bent from a substantially straight configuration to a bentconfiguration having a radius of curvature as small as about 20millimeters. “Kink resistance” of a graft can be determined byutilization of the following protocol, as illustrated in FIGS. 2A, 2Band 2C. In this protocol, the stent graft device 10 with high kinkresistance is curved about a generally circular pin having apredetermined diameter D. The stent graft device 10 tangentiallycontacts the pin at two diametrically opposed portions on the test pinso that the stent graft device 10 defines two parallel substantiallystraight portions having a curve therebetween with an apex coincidentwith the outer surface of the stent graft device at a distance L fromthe closest surface of the pin to the apex, where L is approximately thesame as D (FIG. 2A). A stent graft device 10 that does not kink, asdiscussed above, maintains an effective cross-sectional area proximatethe apex that is essentially the same as the effective cross-sectionalarea for the substantially straight portions of the stent graft device10 (FIG. 2A). More preferably, the effective cross-sectional arearemains constant along the entire length of the stent graft device 10.Therefore, kinking can therefore be defined as the change incross-sectional area proximate the apex of a curved portion as comparedto a substantially straight portion of the device (FIG. 2B). Kinking canbe further defined as the point at which there is a threshold change inthe effective cross-sectional area shown, for example, in FIG. 2C. Morespecifically, kinking results in a loss of cross-sectional areaproximate the apex of the curved portion so as to define across-sectional area that is less than about 50 percent of across-sectional area in a substantially straight portion of the stentgraft device, and is more preferably about 66% of the cross-sectionalarea in the substantially straight portion for a given diameter of thetest pin. It should be noted that the cross-sectional area can bedetermined in a circular cross-section graft by calculating the insidediameter using the formula for circular area (radius squared times theconstant pi). However, for ease of calculations, the outside diameter ofthe graft can be used instead.

An alternative method can be used to determine the presence of kinkingor alternatively the absence thereof in a device using unaided visualcues. For example, to determine whether a stent graft device 10 is kinkresistant, the device can be deployed in a test tube (not shown) havinga radius of curvature of 20 millimeters to observe the behavior of thedevice with regard to the ability to appose the wall of the tube. Whenobserved with an unaided eye, the absence of kinking is apparent byvisual cues such as, for example, the absence of protrusions of strutsto the vessel lumen.

Moreover, for the tubular body 12 to articulate, flex and/or bendwithout substantially kinking, it is to be understood that along thecentral axis A-A in the region the apex of the bend or curvature, theouter and inner curved surfaces 24, 26 defined by the encapsulationsleeve 20 remain substantially equidistant from the central axis A-A, asillustrated in FIG. 2. Because, the outer sleeve 20 does not kink ortwist in response to the bend of the device 10, as discussed above, theinterior dimensions and/or effective cross-sectional area of the tubularbody 12 can remain substantially constant over the length of the deviceso as not to disturb the flow of biological fluids therethrough. Morepreferably, when the stent-graft device is in the bent configuration inthe absence of kinking, the interior 18 of the tubular body 12 continuesto define a substantially circular cross-sectional area along the lengthof the stent-graft device 10.

The outer sleeve 20 is further preferably bonded or coupled to an innersleeve 21 or inner tubular member of graft material to form a monolithicencapsulation of a stent frame 30. The inner sleeve 21 lines theinterior chamber 18 of the tubular body 12 to provide a smooth surfaceover which biological fluids can flow. To facilitate the capability ofthe device 10 to articulate, bend and/or flex without kinking, thesleeve 20 preferably includes a microfold, expansion portion or fold 22that permits the sleeve to elongate and contract in the longitudinaldirection in response to the articulation, bending and/or flexing of thetubular body 12. The device 10 can include multiple expansion folds 22spaced along and radially disposed about the central axis A-A to provideflexibility to the body 12 bent to a radius of curvature. In the regionof the curvature, and more preferably proximate the apex of thecurvature, the expansion folds 22 along the central axis A-A preferablyexpand along the outer curved surface 24 and contract along the innercurved surface 26 in response to the bend of the tubular body 12. Theelongation of the expansion fold 22 and contraction of the expansionfold 22 along the inner surface 26 permits the outer surface 24 and theinner surface 26 to maintain a substantially constant parallel distancerelative to one another over the entire length of the device 10, andthus maintain a substantially constant effective cross-sectional areaover the length of device 10 for a range of radii of curvaturesincluding a radius of about 20 millimeters. Accordingly, the sleeve 20does not show any characteristics that would be considered kinking ortwisting over the length of the device 10 in response to a severe bendconfiguration in the body 12. Therefore for example, where the interiorchamber 18 of the stent graft device 10, in a substantially straightconfiguration, defines the effective cross-sectional area for the device10 through which biological fluids flow, in the bent configuration, theexpansion folds 22 maintain the outer curved surface 24 and the innercurved surface 26 equidistant from the central axis A-A such that theeffective cross-sectional area is maintained. Shown in FIG. 2D is anillustrative effective area 25 of the stent graft 10 at the apex of thecurvature in which the effective area 25 is symmetric about a plane Pbisecting the length of the stent graft device 10.

The tubular body 12 of the stent graft device 10 includes anencapsulated stent frame 30, for example as shown in FIG. 3 in a bare orunencapsulated state. The stent frame 30 of the device 10 provides thestructural rigidity to the stent graft device 10 and also preferablyprovides the device 10 with its flexibility. The stent frame 30 ispreferably constructed of a shape memory alloy. Alternatively, the stentframe 30 can be made out of any type of material besides shape memoryalloy so long as the frame 30 is constructed to bend and flex.Preferably, a plurality of interconnected struts 32 form the stent frame30 including an abluminal surface 34 and a luminal surface 36 of thestent frame 30. The abluminal surface 34 defines the outer surface ofthe device 10 and the luminal surface 36 defines the interior passageway18. Preferably, the stent frame is substantially circular cylindricaland the luminal surface 36 defines a substantially circularcross-sectional area. The plurality of interconnected struts 32preferably intersect and connect at joints 52 disposed along andradially about the central axis A-A. The struts 32 further preferablyinterconnect to form a rhombus or other polygon having an interstice orgap 38 which provide communication between the abluminal surface 34 andthe luminal surface 36. The struts 32 of the stent frame 30 arepreferably interconnected such that the struts 32 can move relative toone another thereby permitting the stent frame to articulate, bendand/or flex.

Although the expansion folds 22 provide flexibility to the stent graftdevice 10, the stent frame 30 can be of any geometry configured tofurther enhance the flexibility of the device 10. Accordingly, variousstent frame designs can be employed. For example, stent frame 30 can beformed as a single unitary piece, or alternatively, the stent frame ispreferably constructed from the plurality of zigzag ring stents 40(stenting zones), as seen in FIG. 3, joined at joining points 52 alongcentral axis A-A. Preferably, there is a joining point 52 between agiven ring stent 40 and an adjacent ring stent 40 every third strut 32with the joining points 52 alternating from the left-hand adjacent tothe right hand adjacent ring stent 40 so that six struts 32 separate thejoining points 52 between any two ring stents 40. Gaps 38 are framed bythe struts 32 and the joining points 52 where the intersections ofzigzag struts are not joined. More preferably, each ring stent 40 isattached to each adjacent ring stent 40 by only a pair of joining points52.

A stent frame 30 as described above is substantially similar to thestent frame of the LUMINEXX, billiary stent, from Bard PeripheralVascular, Inc (hereinafter “Bard”). Alternatively, the stent frame 30can be configured as stent frames used in other known stent graftdevices such as, for example, Memotherm Flexx stents or Flexx stentsalso by Bard. A preferred design for stent frame 30 includes a pluralityof interconnected circumferential zones, ring stents 40, struts orjoints, as shown herein, to form the stent frame with gaps orinterstices between the struts. However, it will be appreciated by thosefamiliar in the art, that the stent frame 30 can have alternativeconfigurations.

The stent frame 30 can, for example, be formed from wire, flat wire, orribbon that is processed and shaped to form a stent frame 30 for use inthe stent graft device 10. More specifically, the stent frame can beformed from a single wire that is bent to form sinusoidal waves or otherperiodic undulations. The wire can then be helically would about acylindrical center to form the stent frame 30. In another helicalarrangement, one or more wires can be weaved into a helical pattern toform the tubular stent frame 30 in which adjacent helical turns of thewire form parallel struts capable of flexible axial movement relative toone another. Alternatively, a stent frame 30 can be formed from theinterconnection of ring stents 40 that are each formed from an axialflat ribbon of wire. To form an individual ring stent 40, the flatribbon of wire can undergo a material removal process so as to form aseries of parallel and staggered slits. The ribbon can be elongated andits transverse ends can be connected to form a ring stent 40 having anundulating wave pattern upon radial expansion. The material removalprocess can be implemented such that the wave pattern has varyingamplitudes along its length. The waves form the struts of the individualring stent 40. Two or more of the ring stents 40 can be interconnectedby one or more strut connectors disposed around the periphery of thestent rings 40 to form the substantially tubular stent frame 30. Theconnectors can be disposed at an angle relative to the central axis toprovide tangential intersection of parallel struts between two adjacentring stents 40. The tangential intersection of parallel struts canaccommodate flexing of the stent within paired struts withoutinterference between adjacent stent segments. In addition, the ringstents 40 can be disposed on and interconnected relative to one anothersuch that the parallel planes defined by the cross-sectional areas ofeach ring stent 40 each define a common angle relative to the centralaxis of the stent frame 30. More preferably, the stent frame 30 isformed from a single tube of material that can undergo a materialremoval process to form the substantially tubular stent frame 30.Material can be removed from the tubular member so as to form a seriesof parallel struts or undulations that are capable of movement relativeto one another to permit expansion of the stent frame 30. The materialremoval process can form undulating sign waves of constant or varyingamplitude; alternatively, the material process can form helical turnsalong the axial length of the tubular member. For example, a spiralstent frame 30 can be formed from a single tubular member in whichspiral, helical or other continuous voids are cut into the tubularmember to form the stent frame having interstices along its length.Generally, the material removal process can form any pattern in thetubular member that provides for adjacent struts that can move relativeto one another to permit expansion and flexing in the stent frame 30.Exemplary alternative configurations of the stent frame 30 that can beused in stent graft device 10, including those described herein, areshown and further described in the following patent documents: U.S. Pat.No. 5,899,935; U.S. Pat. No. 6,551,351; U.S. Pat. No. 6,656,219; U.S.Pat. No. 6,923,828; U.S. Pat. No. 5,507,767; U.S. Pat. No. 5,800,456;U.S. Pat. No. 6,059,808; U.S. Pat. No. 6,013,854; U.S. Pat. No.6,010,530; and U.S. Pat. No. 6,238,409.

Again referring to the stent frame 30 of FIG. 3, the interstices or gaps38 between the joining points 52 permit the struts 32 to move relativeto one another thereby making the stent frame 30 flexible forarticulation or bending. The gap 38 defines an initial gap length whenno load is placed on the stent device 10, i.e. when the stent device 10is neither under tension nor compression. A stent ring 40 in the no loadstate, as seen for example in FIG. 4A, defines the gap 38 having anaxial gap length s. The axial gap length s can be measured between anytwo points of the stent region or ring 40 that are opposite one anotherabout an imaginary central axis C-C. For example, the axial gap lengthcan be measured between points 33 a and 33 b located at the two innermost apexes of the stent ring 40, but alternatively and preferably, theaxial gap length is measured between the outer most apexes of the stentring 40, at points 33 c, 33 d. Preferably, the initial axial gap lengths in a stent ring 40 in a no load state is preferably about 0.15millimeters, but the axial gap length s can range from as much as about3 to about 6 millimeters, preferably between about 3 and 5 millimetersand can be about 3.7 millimeters. A gap height of gap 38 can be definedby two points such as, for example, points 35 a, 35 b of the stentregion or ring 40 that are opposite one another about the an imaginaryaxis D-D parallel to the central axis A-A. In addition, the zig-zagstruts 32 can define one or more initial included angles, angle α andangle β which vary with the contraction and elongation of the stentframe as it moves between a substantially straight configuration to asubstantially bent configuration. The included angles α, β can furtherquantify or define a characteristic configuration of the stent ring 40and gap 38. Accordingly, because various stent frames can be employed,the struts 32 and stent ring points 33 a, 33 b, 35 a, 35 b defining thegap lengths, gap heights and included angles may vary and can bemeasured from various reference points and/or angles.

When the stent graft device 10 is bent in a curved configuration. Theouter curved surface 24 and the inner curved surface 26, relative to thecenter of curvature, are respectively in tension and compression.Accordingly, the portion of the stent ring 40 located on the outercurved surface 24 is under tension, and conversely the portion of thestent ring 40 located along the inner surface 26 is under compression.When the stent ring 40 is under compression, the axial gap length isless than when the gap is under no load or in tension. When the stentring 40 is under tension, as shown in FIG. 4B, the axial gap length swidens along the axis of elongation by a change in length of an amount bso as to define a total axial gap length s+b. The increase in the gaplength b is equal to about five to twenty percent of the gap length inthe no load condition, preferably is about five to about ten percent,and more preferably about seven percent of the gap length in the no loadstate. Preferably, the axial gap length s+b is at its maximum when thestent ring 40 is located at the outer curved surface 24 at the apex of aradius of curvature of about 20 millimeters, i.e. a preferred minimumstent radius. The increased axial gap length when the stent is intension can range from about 0.15 millimeters to about 0.5 millimetersdepending upon the original gap length.

A lengthwise cross-sectional view of an illustrative embodiment of thestent graft device 10 is shown in FIG. 5A. The encapsulation sleeve 20of the stent device 10 preferably includes one or more microfolds,expansion portions or folds 22 spanning at least one gap 38 of the stentframe 10. The expansion folds 22 provide kink resistance to the stentgraft device 10 by enabling the axial expansion and contraction of thesleeve 20 in response to the relative movement of the struts 32. Inaddition, the expansion folds 22 of the graft material along the outersurface of the stent graft device 10 can define one or morelongitudinally extending undulations along the length of the stent graftdevice 10.

An undulation can be a portion of the expansion fold 22 formed by thegraft material spanning the gap 38 of the stent frame 30 so as to haveat least one of a peak and a valley. Preferably, the undulations areconfigured and disposed uniformly along the length of the device 10 soas to evenly distribute the graft material. The even distribution of thegraft material can minimize the profile of the stent graft device 10 bypreventing areas of concentration of graft material along the outersurface. A preferred undulation can be formed where the length of theexpansion fold 22 is about 5-20 percent longer than the gap length ofthe gap 38, preferably about 5-10 percent longer and more preferablyabout 7 percent longer than the length of gap 38. With the stent graftdevice 10 in the bent configuration, the outer curved surface 24preferably does not include an undulation as the length of the expansionportion 22 is about equal to the arc formed by the axial length of thegap 38. Accordingly, the undulations can appear and disappear from theprofile of the stent graft device 10, as the device 10 articulatesand/or flexes through a range of curvatures.

The minimized profile of the stent graft device, when in the straightconfiguration, can further minimize the resistance experienced whenloading the device 10 into a stent delivery device such as a catheter orsheath. Preferably, the minimized profile permits the stent graft to beloaded into reduced size sheath. For example, where known stent grafthaving a diameter of 10 millimeters and a length of 100 millimeters,i.e. a 10/100 stent graft device was loaded into a 9 French (F) sheath,a stent device configured according to the preferred embodiment producesa profile capable of being loaded into an 8 F sheath. Moreover, thepresence of the expansion folds 22 in the stent device 10 allows thedevice 10 to be loaded into a sheath with minimized force as theexpansion folds 22 permit contraction of the device 10 therebyminimizing the resistive force to loading. More specifically, theexpansion folds absorbs the loading force that would normally add to theaxial stress in the stent frame. In addition, the expansion folds 22 actas a beading on the stent graft device 10 by reducing the line contactwith the sheath.

The expansion fold 22, being configured to expand and contract axiallywith the expansion and contraction of the stent frame 30, provides theflexibility of the device 10. Thus, where the gap 38 widens along thecentral axis in response to the bending of the stent frame 30, theexpansion portion 22 unfolds or elongates in the same direction by acorresponding arc length. In addition, where a gap 38 of the stent frame30 contracts in response to the same bend, the covering expansionportion 22 contracts accordingly. Because the encapsulation sleeve 20can expand and contract with the stent frame 30 via the expansionportions 22, the outer sleeve can articulate, bend and/or flex with ahigh kink resistance.

Again referring to FIG. 5B, shown is an illustrative embodiment of thestent graft device 10 in a bent configuration such that the outer sleeve20 defines a radius of curvature, preferably of about 20 millimeters.More specifically, shown is an expansion fold 22 having expansionportions 22′, 22″ respectively on the outer and inner curved surfaces24, 26 of the stent device 10 in corresponding expanded and contractedstates. The absence of kinking in any stent graft device 10 necessarilyprovides that the graft material on the inner curved surface 26 axiallycontracts by a length equal to the outer amount by which the graftmaterial on the outer curved surface 24 axially lengthens.

In the bent configuration, the points 33 a′, 33 b′ further define achord of a circle having a radius equal to the radius of curvature forthe bent configuration. The chord is substantially equal to the expandedgap length between 33 a′ and 33 b′, for example, s+b. In one embodiment,the arc length l defining the minimum length of the expansion portion22′ is about equal to the expanded gap length s+b and therefore, asdescribed above, is substantially equal to about 105-120 percent of gaplength s, preferably about 105-110 percent of gap length s, and morepreferably about 107 percent of gap length s. In the bent configuration,the points 33 a′, 33 b′ of the frame 38 further defines an angle θ whichcan be approximately solved for from the relation:

sin(θ/2)≈(s+b)/(R+D)

Preferably, the expansion portions 22′, 22″ have an axial length atleast as long as arc length defined by a the maximum length of the gap38. For example, the expansion portion 22′ has an axial length l,preferably substantially equal to the arc length defined by opposingpoints of a stent region or ring 40, i.e., points 33 a′, 33 b′ at theirmaximum axial gap length such as where, for example, the stent device 10is in a bent configuration having a radius of curvature of about 20millimeters. Conversely, the points 33 a″, 33 b″ along the inner curvedsurface 26 are in a maximum contracted configuration. Preferably, theradius of curvature is measured from the outer curved surface 24although the radius of curvature could be measured from anotherreference line, for example, from the central axis A-A or the innercurved surface 26. With the stent device in its severe curvatureconfiguration, the expansion portion 22′ along the outer curved surface24 is preferably longitudinally expanded such that the expansion portion22′ was substantially parallel to the central axis A-A over the lengthof the expansion portion 22. More preferably, the expansion portion 22″along the inner curved surface is contracted so as to form at least oneundulation over the length of the curvature.

In order that the expansion portions 22′, 22″ expand and contract to theproper length so as to avoid kinking, and therefore maintain theeffective cross-sectional area of the stent graft device 10, theexpansion portions 22′, 22″ must have an appropriate axial lengthrelative to the length of the gap 38 in the stent frame 30. A preferredmethod of forming the stent-graft device 10 and its expansion portions22 generally provides elongating the stent frame 30 from an initialaspect ratio to define a second aspect ratio before encapsulating thestent frame 30 in graft material. Accordingly, the method of formationfurther provides affixing a tubular graft member to or concentricallyabout the stent frame 30 in its elongated state, and relaxing theassembly such that the stent frame 30 returns or contracts to define athird aspect ratio, the third aspect ratio generally being in the rangebetween the first and the second aspect ratio.

The aspect ratio of a stent frame 30 can be defined as the ratio of thestent frame length to the stent frame diameter. The aspect ratio of anunloaded stent frame, i.e. under neither tension nor compression, canvary. For example, the aspect ratio (length to diameter ratio)determined in millimeters of an unloaded stent frame can be: 40:5;120:5; 120:7; 120:8; 120:9; 120:10; 40:12 and 40:13.5. Generally, as thestent frame is axially compressed or elongated, the diameter of thestent frame correspondingly increases or decreases in response and/orsubject to external constraints to radial expansion/contraction of thedevice. Thus, as the length of the stent frame 30 is elongated orcontracted the stent frame 30 aspect ratio may accordingly be altered.Alternatively or in addition to, the aspect ratio can be defined at thelevel of the stent region or ring 40. For example, the aspect ratio ofthe stent frame 30 can be defined by the ratio of the gap width to gapheight of an individual stent ring 40. Elongation of the stent frame 30will increase the gap length, and due to the interconnection of struts32, the gap height of the stent ring 40 will respond accordingly therebyaltering the aspect ratio of the stent. Alternatively, where thediameter remains constant during elongation, the included angles varyaccordingly. For example, the included angles α, β enlarge due to anelongation of the stent frame 30.

As already noted, the preferred method includes elongating a stent frame30 to expand the gap length of the gaps 38 in the axial direction toalter the aspect ratio of the stent graft device 10 from an initialunloaded condition to a second aspect ratio. With the stent frame in theelongated state, a tubular graft member is bonded to the stent frame,preferably to the outside of the stent frame 30 or to the inside of thestent frame 30. Preferably, the tubular graft member forms the outersleeve 20 and is bonded to an inner sleeve 21 of the graft memberdisposed within the interior of the stent frame 30 so as to encapsulatethe stent frame 30 between the inner and outer tubular graft members.Alternatively, the outer and inner sleeves 20, 21 can encapsulate thestent frame using sutures, ultrasonic welding, stapling, and adhesivebonding etc. It is also possible that a single tubular graft member 21is coupled to the stent graft 30, for instance positioned coaxiallyinside the stent frame 30. In such a case it is preferable that thetubular graft member 21 is secured to the luminal surface 36. Such anembodiment will be further discussed below with reference to FIG. 7.Preferably, the outer and inner sleeves 20, 21 are made of ePTFE, butother biocompatible materials are possible including ultra thin wallmaterial (UTW) ranging in thickness from about 0.08 millimeter to about0.25 millimeter, regular thin wall material (RTW) ranging in thicknessfrom about 0.3 millimeter to about 0.8 millimeter, polyamides,polyimides, silicones, fluoroethylypolypropylene (FEP)polypropylfluorinated amines (PFA), or other fluorinated polymers. Thetubular graft members 20,21 when made of ePTFE are made by extruding aPTFE-lubricant mixture through a ram extruder into a tubular shapedextrudate and longitudinally expanding the tubular shaped extrudate toyield a uniaxially oriented fibril microstructure in which substantiallyall of the fibrils in the ePTFE microstructure are oriented parallel toone another in the axis of longitudinal expansion, as is known in theart and described in U.S. Pat. Nos. 3,953,566; 4,187,390; and 4,482,516which are attached hereto respectively as Exhibits C, D, and E and arefurther expressly incorporated by reference as teaching a method ofmaking longitudinally expanded PTFE extrudates.

The use of unsintered of partially sintered ePTFE tubular extrudates ispreferable over fully sintered ePTFE materials, whether in tubular formor in sheet form. The partially sintered ePTFE has a microstructurewhich is substantially undisturbed during processing and assembly of thestent graft 10 until the final step of fully sintering the ePTFE toencapsulate the stent. The stent encapsulation results in spans ofbonded graft material covering the expanded gaps 38 in the stent frame30. Additionally, or alternatively, the outer graft member 20 or theinner graft 21 is secured to the stent frame 30 on the basis of anintervening polymeric bonding layer, preferably applied to the stentframe 30 prior to coupling the tubular graft member 21 to the stentframe 30. Such an embodiment is further discussed below with referenceto FIG. 9.

The method of formation further provides relaxing the assembled stentgraft device such that the stent frame is permitted to contract axially.As the stent frame contracts from the elongated state, the encapsulatinggraft material contracts with the stent frame and the spans of graftmaterial between the gaps 38 or interstices form the expansion folds 22of the stent graft device 10.

One embodiment of the preferred method of forming the stent device 10initially provides loading a first tubular graft member 21 about amandrel and securing the member at both ends. For example, the graftmember 21 can be seven millimeter (7 mm.) carbon lined UTW graft orother bio-compatible material, and the forming mandrel is preferably a6.6 millimeter hollow stainless steel mandrel. More preferably, thegraft material is a tubular member formed of ePTFE previously asdescribed herein. In a second step, a stent frame 30 is disposed aboutthe first tubular graft material located on the mandrel. Preferably, thestent frame 30 is an 8×50 AV access stent having a flared and non-flaredend, or alternatively, the stent frame 30 can be of anotherconfiguration such as, for example, any stent frame previously describedherein. The non-flared end is preferably secured to the mandrel, and thestent frame 30 is then elongated over the inner or first tubular graftmember 21. Preferably, the stent frame 30 is elongated such that thegaps 38 have a gap length of about 0.5 millimeters and the overall stentframe length is about 59 millimeters. Generally, the stent frame 30 iselongated so as to increase the stent frame 30 by about five to abouttwenty percent, preferably about five to about ten percent, and morepreferably about seven percent. With the stent frame in an elongatedstate, the flared end can be secured to the mandrel. Preferably, thedistance from the end of the mandrel to the end of the flare isdetermined to define an offset. More preferably, the distance from theend of the mandrel to the end of the flare defines an offset of about130 millimeters. In a third step, an outer or second tubular graftmember is disposed over the elongated stent and secured at both endsthereby forming a graft-stent-graft assembly. Preferably, the secondtubular graft member is approximately 7 millimeter graft material. Tosecure the second tubular graft member, a TEFLON (TFE) tape ispreferably applied at each end.

In a fourth step, a wrapping is preferably applied to the length of theassembly. In a preferred wrapping process, the outer tubular graftmember 20 is tensioned about the stent frame 30 to form a bond with theinterior tubular graft member 21. Preferably, a wrap tension of about900 gram force (900 gf.) is applied. The bond is formed in the gaps 38of the stent frame 30. The wrapping can be performed by placing themandrel, with the stent graft stent assembly disposed about the mandrelin a spiral machine and applying an appropriate tensioning voltage.Alternatively, the wrapping process can be applied by known techniquesin the art. Voltage and speed settings can be provided to the spiralmachine to effect a desired wrap and bond. Preferably, the wrapping isapplied over the length of the assembly at an adequate voltage and atadequate traverse and spindle speeds to effect the desired wrap andbond. The wrapping is preferably stopped to remove the tape securing thenon-flared end of the stent. In addition, the wrapping process ispreferably applied twice over the length of the assembly, in which thetape removal occurs after the first pass. Preferably, there is anoverlap of the wrap of about 2.0 to 2.5 millimeters, preferably about2.31 millimeters. With the tape removed from the non-flared end, theremainder of the assembly can be wrapped. In a fifth step, the flaredend is released by cutting back a portion of the graft material.Preferably, the graft material is cut back to a location that is about10 millimeters internal to the measured offset from the loadingprocedure described above. In a sixth step of the preferred method, theassembly is sintered to bond the first tubular graft member to thesecond tubular graft member. The assembly can be removed from themandrel once the assembly has cooled. In a finishing process, theencapsulating graft material can be cut back by laser cutting. Apreferred laser cutting machine is, for example, laser cutting machinemodel number ULS-25PS from UNIVERSAL LASER SYSTEMS, INC. Preferably, theencapsulation material is cut back 10 millimeters internal of the flaredend and the 1 millimeter external to the non-flared end. Preferably, thelaser cut is performed in spiral machine having an 8 millimeter spiral,at 75% speed, 50% power, 330 ppi with the object height set to 6 inchesplus ½ diameter of the cutting mandrel (6.125 inches). Shown in FIG. 6is a illustrative flow chart of this preferred method. In an alternativemethod, is a tubular graft member 21 coaxially positioned inside thestent frame 30 and, for instance, secured to the luminal surface 36 ofthe tensioned stent graft 30. The graft member 21 can be secured to thestent frame 30 on the basis of an intervening polymeric bonding layer.Such a layer is applied by powder coating or holding the stent frame 30in a liquid containing a polymer. The polymer can be PTFE, PET, FEPetc., or any other fluoropolymer. Instead of bonding the inner graftmember 21 to outer graft member 20, in this method the inner graftmember 21 is during heating, for instance fusing or sintering, bonded tothe polymer coating applied to the stent graft 30. Other steps of thisalternative method are similar to the steps followed for forming anencapsulated stent graft 30. This embodiment is further discussed belowwith reference to FIG. 9.

In one aspect of the preferred method, the elongation of the stent frame30 over the first tubular graft member 21 is made such that the stentframe is elongated to an extreme length. More specifically, the stentframe 30 is elongated from about 50 millimeters to a length of at leastabout 64 millimeters. In another aspect of the method, the first orinner graft member 21, stent frame 30 and outer graft member 20 aremounted and secured to the mandrel with the stent frame 30 elongated tothe extreme length, as previously described. The assembly is thenwrapped; stopping long enough to remove the TEFLON tape securing thestent frame. The assembly is then wrapped a second time and thensintered. The assembly is laser cut 10 millimeters from the flared endto release the flare and then the assembly is sintered for an additionalperiod of time. The wrapping process of the method can be furthermodified to effect the bonding between the inner tubular graft memberand the outer tubular graft member. For example, the graft-stent-graftassembly can be disposed and secured about the mandrel and a voltage of18 volts can be applied. In addition, the assembly can be wrapped threetimes.

The methods of forming the stent graft device 10 can be further modifiedby the application of TEFLON tape to the graft-stent-graft assemblyprior to sintering in order to control the bond between the inner graftmember 21 and outer graft member 22. For example, a band of TEFLON tapecan be applied to the circumference of the graft-stent-graft assembly ina manner that avoids the gaps 38 of the stent frame 30. Once the TEFLONtape is secured about the circumference of the assembly, the assemblycan be sintered. In another embodiment of the method, the TEFLON tapecan be applied to the ends of the assembly. The TEFLON tape can belimited to application at the stent rings 40 at the ends of theassembly, thus leaving the central portion of the assembly unwrapped.The assembly with the TEFLON tape at its ends can be sintered to producea stent graft device 10 having ends with a smaller diameter than thecentral portion of the device. In addition, the unwrapped portion of theassembly can leave the inner graft member unbonded to the outer graftmember.

In yet another embodiment of the method of forming the stent graftdevice 10, the outer tubular graft member can be further configured toincrease flexibility in the device 10. For example, the outer graftmember can be slit in the areas spanning over the gaps 38 in theunderlying stent frame 30, and then graft-stent-slitted graft assemblycan be wrapped as described, for example, at 10 volts and sintered for11 minutes. Further in the alternative, the outer graft member can beapplied as a plurality of elongated strips radially distributed aboutthe elongated stent frame 30 in a manner as described in U.S. Pat. No.6,558,414 which is incorporated herein in its entirety.

In an embodiment the stent frame 30 is coated with a polymeric bondinglayer 100. Such a polymer coating may be of polytetrafluoroethylene(PTFE), fluorinated ethylene propylene (FEP),polytetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA),polyvinyl chloride (PVC), polypropylene (PP), polyethylene terephthalate(PET), polytuinylidene fluoride (PVDF) and other biocompatible plastics.Methods of applying such a coating 100 to the struts 32 of stent graft30 are described in WO 98/00090 and include immersing the stent graft 30in a vessel containing an aqueous dispersion of such a polymer, forinstance PTFE. This is also known as dip coating as described in EP1164972 B1. Numerous ways of spraying techniques may alternatively beemployed. It is for instance possible to apply an electrostatic sprayprocess in which a coating powder is withdrawn from a reservoir in anairstream and electrostatically charged in a high voltage corona of aspray gun. This method as well as plasma coating is also described in EP1164972 B1. The tubular graft member 21 is coaxially positioned insidethe stent frame 30 and secured to the stent frame 30 on the basis of theintervening polymeric bonding layer 100. A stent frame 30 with a singlegraft member 21 bonded to a luminal surface 36 of the stent frame 30 isusually radially contractable to a diameter which is less than thediameter to which a stent graft 30 as encapsulated between an innergraft member 21 and an outer graft member 20.

With reference to FIG. 8A and FIG. 8B, which show a detail of aschematic view of the stent frame 30 provided with inner graft member21, of which a cross sectional view is provided in FIG. 7, it is pointedout that a gap G between two opposite apexes 102 can easily be 5% largerin a stretched stent graft assembly according to FIG. 7, as compared tothe length of the gap G between the apexes 102 in an unstretched stentgraft assembly according to FIG. 7.

An example of a method for making a stent graft device having graftmember 21 coupled the abluminal surface 36 of stent frame 30 isschematically outlined in FIG. 9. A graft member 21 may be dilated andloaded onto a mandrel. Preferably, the graft member comprises tubularlyshaped unsintered PTFE. Both ends of the tubular graft layer are securedto the mandrel. A stent graft 30 is disposed about this unsintered PTFEgraft member. The stent graft concerns a stent graft which has beencoated with a bonding polymer, preferably a fluoropolymer, for instanceby methods as discussed above.

A first end of the stent is secured to the mandrel, for instance by awell-known wrapping method.

The stent is elongated from a second end of the stent and the second endis also secured to the mandrel. The next step concerns wrapping PTFEtape on the outside of the stent for pressing the inside of the stentradially inwards so that the fluoropolymer coating at the inner side ofthe stent is pressed against the outside of the unsintered PTFE graftlayer. The stent graft assembly is then sintered, at a temperature of370° C. and for a time which is shown to lead to bonding of the stentgraft to the stent graft member. A suitable time was found to be about10 minutes. After, or during, cooling down, the PTFE tape can beunwrapped from the stent graft assembly. The elongated graft assemblycan be removed from the mandrel and relax. It is then possible to triman overhang of the inner graft member 21 to the stent frame 30.

EXAMPLE ONE

In a first example of manufacturing a stent graft device 10 according tothe preferred method, a first 7 millimeter carbonlined inner UTW graftmember was loaded onto a stand, and a 7.7 millimeter solid aluminumloading mandrel was inserted into the graft member to load the graftmember on the mandrel. The ends of the first graft member were securedto the mandrel by TFE tape. An 8×50 millimeter stent having a flared endand a non-flared end was loaded onto the outside of the first graftmember and centered. The non-flared end was secured to the mandrel byTFE tape and the stent was slightly elongated. The distance from the endof the mandrel to the end of the stent at the flared end was measured. Asecond 7 millimeter UTW graft member was loaded over the elongatedstent, and both ends of the second graft member were secured. Themandrel assembly was placed in a spiral machine and a wrapping processwas applied. More specifically, a circumferential pressure or tensionwas applied to the assembly to cause the first and second graft membersto come into contact through the interstices of the stent frame. Thewrapping process was stopped at point along the assembly to permitremoval of the TFE tape, and the wrapping process was completed alongthe length of the assembly. The assembly was cut back by laser cuttingthe assembly at the flared end to release the flare. Preferably, theflared end was cut back at about 10 millimeters. The assembly was thensintered resulting in a flexible stent graft device. Notably, lasercutting the assembly before sintering resulted in an assembly in which20 millimeters of the original 50 millimeter stent contracted to itsoriginal pattern at the flared end, the remainder maintained anelongated configuration.

EXAMPLE TWO

In a second method of manufacturing a stent graft device 10, a 7millimeter carbon lined inner UTW graft member was loaded onto a 6.6millimeter hollow stainless steel mandrel and the ends of the firstgraft member were secured to the mandrel. An 8×50 millimeter stenthaving a flared and non-flared end was placed on the mandrel andcentered. The non-flared end of the stent was taped to the mandrel, andthe stent was extremely elongated such that the stent reached a lengthof about 64 millimeters. The assembly is placed in a spiral wrappingmachine and a wrapping process is applied to the length of the device,stopping short to remove the tape from the non-flared end. The wrappingprocess is continued to completion with the entire assembly beingwrapped. The assembly was sintered and laser cut from the flared end, atabout 10 millimeters from the flared end of the device, in order torelease the flare. The assembly was then additionally sintered. Thisexemplary method produced a stent graft device that contractedlongitudinally, but became rather rigid due to the second sinteringcycle.

EXAMPLE THREE

In a third method of manufacturing a stent graft device 10, a 7millimeter carbon lined inner UTW graft member was loaded onto a 6.6millimeter hollow stainless steel mandrel and the ends of the firstgraft member were secured to the mandrel. An 8×50 millimeter stenthaving a flared and non-flared end was placed on the mandrel andcentered. The non-flared end of the stent was taped to the mandrel, andthe stent was extremely elongated such that the stent reached a lengthof about 64 millimeters. The assembly is placed in a spiral wrappingmachine and a wrapping process is applied to the length of the device,stopping short to remove the tape from the non-flared end. The wrappingprocess is continued to completion with the entire assembly beingwrapped. The assembly was sintered and laser cut from the flared end atabout 10 millimeters from the flared end of the device in order torelease the flare.

EXAMPLE FOUR

A fourth example of manufacturing a stent graft device 10 substantiallysimilar to the method used in Example One provided, a first 11millimeter carbon lined inner UTW graft member was loaded onto a stand,and a 10.7 hollow stainless steel mandrel was inserted into the graftmember to load the graft member on the mandrel. The ends of the firstgraft member were secured to the mandrel by TFE tape. An 12×80millimeter Iliac stent having a flared and a non-flared end was loadedonto the outside of the first graft member and centered. The non-flaredend was secured to the mandrel by TFE tape and the stent was slightlyelongated and then secured at the flared end. The distance from the endof the mandrel to the to the end of the stent at the flared end wasmeasured then secured at the flared end. A second 11 millimeter UTWgraft member was loaded over the elongated stent, and both ends of thesecond graft member were secured. The mandrel assembly was placed in aspiral machine and a wrapping process was applied. More specifically, acircumferential pressure was applied to the assembly to cause the firstand second graft members to come into contact through the interstices ofthe stent frame. The wrapping process was stopped to permit removal ofthe TFE tape at the non-flared end, and the wrapping process wascompleted along the length of the assembly. The assembly was cut afterlamination to release the flare at the flared end. Preferably, theflared end was cut back at about 10 millimeters. The assembly was thensintered resulting in a stent graft device exhibiting some flexibility.However, the gaps of the stent frame moved to about 0.5 millimetersapart, and there was limited uniformity in the shape of the gaps of thestent frame.

EXAMPLE FIVE

A sample run of six stent graft devices produced by an embodiment of thepresent method were generated to evaluate the flexibility of the sampledevices in addition to the ability of the sample to return to theiroriginal length after assembly. Each of the six test samples wereproduced by providing a first 7 millimeter carbon lined inner UTW graftmember loaded onto a stand, and a 6.7 hollow stainless steel mandrel wasinserted into the graft member to load the graft member on the mandrel.The ends of the first graft member were secured to the mandrel by TFEtape. An 8×50 millimeter Beta I Memotherm stent having a flared and anon-flared end was loaded onto the outside of the first graft member andcentered. The non-flared end was secured to the mandrel by TFE tape andthe stent was slightly elongated to a point 130 millimeters from the endof the mandrel. A second 7 millimeter UTW graft member was loaded overthe elongated stent, and both ends of the second graft member weresecured. The mandrel assembly was placed in a spiral machine and awrapping process was applied. More specifically, a circumferentialpressure was applied to the assembly to cause the first and second graftmembers to come into contact through the interstices of the stent frame.The wrapping process was stopped at point along the assembly to permitremoval of the TFE tape, and the wrapping process was completed againalong the length of the assembly. The wrapping process was applied twiceto the assembly. The assembly was cut back by laser cutting the assemblyat the flared end to release the flare. Preferably, the flared end wascut back at about 10 millimeters, and the assembly was then sintered.

To evaluate impact on elongating the stent frame to the final stentgraft device, measurements were taken at three instances during assemblyfor the sample device. First, an initial length of the stent frame wastaken prior to assembly. A second measurement was taken at theelongation of the stent frame; and a final measurement was taken afterthe assembled device was removed from the mandrel following sintering.Table 1 below shows a range of measured initial, elongated recoveredstent lengths for an array of stent graft devices produced by thepreferred method.

TABLE 1 Stent Graft Device Initial Stent Frame Elongated Stent FrameRecovered Length (in Length (in millimeters) Length (in millimeters)millimeters) 50.4 58.95 55.1 50.6 57.68 54.6 50.5 59.0 55.8 50.7 58.69n/a 50.6 60.5 57.0 50.5 58.98 55.9 50.5 59.0 56.0 50.5 58.85 56.0

Preferably, the initial stent frame is elongated by about fifteen toabout twenty percent (15%-20%) of its initial length. When the stentgraft device is removed from the mandrel, the stent frame is relaxed andpermitted to recover or contract axially. As indicated by the summarytable provided, a stent device 10 can contract to a length that rangesfrom about one hundred ten percent to about one hundred fifteen percent(110%-115%) of the initial stent frame length, and preferably is aboutone hundred twelve percent (112%) of the initial stent frame length,depending upon the amount of elongation. Preferably, the stent graftdevice 10 would recover or rebound from the fully elongated stent framelength to the initial length of the stent frame. However, due to thepresence of the graft material, the stent graft device experiences arebound ranging from about thirty to about fifty percent (30%-50%) ofthe elongation length which is the length difference between the initialstent length and the fully elongated stent length. Accordingly, theassembled stent graft device 10 includes an expansion length which isthe difference between the relaxed and recovered state and the fullyelongated state. This expansion length can range from about five percentto about ten percent (5%-10) of the relaxed and recovered length of thestent graft device 10 and is preferably about seven percent (7%) of therelaxed and recovered length of the stent graft device. This expansionlength preferably provides the stent graft device 10 with itsflexibility and kink resistance.

The expansion length can provide flexibility in the device in at leastone aspect by compensating for the foreshortening effect experienced bythe stent frame 30 as its inner chamber 18 goes from a collapsed stateto a dilated state. For example, an non-elongated stent frame 30 in acollapsed state such as when configured for loading in a stent deliverydevice, has a gap 38 with a gap length at its maximum. When the stentframe 30 is dilated, for example, about a mandrel, the gap length of gap38 is reduced. This reduction in gap length can range from about five toten percent (5%-10%) and is preferably about seven percent (7%).Accordingly, to provide a stent graft device with a flexibility thatresists kinking, it is preferred to provide an expansion length of aboutfive to ten percent (5%-10%) and preferably about seven percent (7%)that compensates for any foreshortening experienced when bending thestent graft device 10.

The dimensions of the graft material, stent frame and dilating mandrelcan also be altered in any of the methods described herein to producevarious embodiments of the stent graft device 10. For example, thedimensions of the graft material, stent frame, and mandrel can beenlarged to produce larger diameter and longer stent grafts. In oneembodiment, the stent frame is preferably a 12 millimeter Iliac stentcut to 80 millimeters in length. The stent frame is preferably disposedbetween two 11 millimeter UTW inner carbon graft members or morepreferably between two ePTFE members. The stent frame and graft membersare further preferably assembled upon a 10.7 millimeter hollow stainlesssteel mandrel to produce a longer and larger diameter stent graft device10. The methods described herein can use a tapered mandrel as describedin U.S. Pat. No. 6,214,039 which is incorporated herein in its entiretyby reference thereto and attached hereto as Exhibit F. Alternatively,other dilating mandrels or devices known in the art that radially expandtubular grafts and stent frames can be used as well.

The mandrel can also be further configured to control the bond betweenthe inner graft member and the outer graft member of the assembly. Forexample, the mandrel can include a spline to form alternating rings ofbonded and unbonded graft material along the length of the stent graftdevice 10. More specifically in a method of forming the stent graftdevice 10, the inner graft member and stent frame can be disposed abouta mandrel having a spline. The stent frame can be axially elongated onthe mandrel such that the gaps 38 of the stent frame 30 are disposedover the splines of the mandrel, and the joints 52 aligned with thesplines. Alternatively, the joints can be off-set with respect to thesplines of the mandrel. With the stent frame aligned with respect to thesplines, the outer graft member can be disposed about the innergraft-stent frame assembly and secured. The graft-stent-graft assemblycan be wrapped, for example, at 10 volts and subsequently sintered at370° C. for 11 minutes.

The method of forming the stent graft 10 can also be further modified byaltering the wrapping process including altering the spindle speedand/or the tensioning voltage of the spiral machine used in the process.The spindle speed can range from about fifty to about eighty centimetersper minute and is preferably about seventy centimeters per minute (70cm/min). The voltage effecting the tension force of the outer tubulargraft member 20 about the stent frame 30 in order to bond with the innertubular graft member 21 can range from about ten to about twenty voltsand preferably ranges from about ten to about fifteen volts (10V-15 V).In addition, the sintering process can be modified by altering thesintering temperatures and/or sintering times. The stent graft assemblycan be sintered at a temperature ranging from about 350° C. to about375° C. and is preferably about 370° C. The sintering time can dependupon the sintering temperature, where, for example, the sinteringtemperature is about 370° C., the sintering time can range from aboutten to about fifteen minutes and is preferably about eleven minutes.Generally, the wrapping and sintering processes or steps describedherein can be conducted and/or modified in any manner provided theysufficiently encapsulate and bond the outer and inner graft members 20,21 about the stent frame 30.

The graft material used in either sleeve 21 or outer sleeve 22 can bevariably configured so as to include such features as, radiopacityand/or bioresorbablility. For example, bio-active agents can beincorporated with the implantable prosthesis. The agents include (butare not limited to) pharmaceutic agents such as, for example,anti-proliferative/antimitotic agents including natural products such asvinca alkaloids (i.e. vinblastine, vincristine, and vinorelbine),paclitaxel, epidipodophyllotoxins (i.e. etoposide, teniposide),antibiotics (dactinomycin (actinomycin D) daunorubicin, doxorubicin andidarubicin), anthracyclines, mitoxantrone, bleomycins, plicamycin(mithramycin) and mitomycin, enzymes (L-asparaginase which systemicallymetabolizes L-asparagine and deprives cells which do not have thecapacity to synthesize their own asparagine); antiplatelet agents suchas G(GP) IIb/IIIa inhibitors and vitronectin receptor antagonists;anti-proliferative/antimitotic alkylating agents such as nitrogenmustards (mechlorethamine, cyclophosphamide and analogs, melphalan,chlorambucil), ethylenimines and methylmelamines (hexamethylmelamine andthiotepa), alkyl sulfonates-busulfan, nirtosoureas (carmustine (BCNU)and analogs, streptozocin), trazenes—dacarbazinine (DTIC);anti-proliferative/antimitotic antimetabolites such as folic acidanalogs (methotrexate), pyrimidine analogs (fluorouracil, floxuridine,and cytarabine), purine analogs and related inhibitors (mercaptopurine,thioguanine, pentostatin and 2-chlorodeoxyadenosine {cladribine});platinum coordination complexes (cisplatin, carboplatin), procarbazine,hydroxyurea, mitotane, aminoglutethimide; hormones (i.e. estrogen);anti-coagulants (heparin, synthetic heparin salts and other inhibitorsof thrombin); fibrinolytic agents (such as tissue plasminogen activator,streptokinase and urokinase), aspirin, dipyridamole, ticlopidine,clopidogrel, abciximab; antimigratory; antisecretory (breveldin);anti-inflammatory: such as adrenocortical steroids (cortisol, cortisone,fludrocortisone, prednisone, prednisolone, 6α-methylprednisolone,triamcinolone, betamethasone, and dexamethasone), non-steroidal agents(salicylic acid derivatives i.e. aspirin; para-aminophenol derivativesi.e. acetominophen; indole and indene acetic acids (indomethacin,sulindac, and etodalac), heteroaryl acetic acids (tolmetin, diclofenac,and ketorolac), arylpropionic acids (ibuprofen and derivatives),anthranilic acids (mefenamic acid, and meclofenamic acid), enolic acids(piroxicam, tenoxicam, phenylbutazone, and oxyphenthatrazone),nabumetone, gold compounds (auranofin, aurothioglucose, gold sodiumthiomalate); immunosuppressives: (cyclosporine, tacrolimus (FK-506),sirolimus (rapamycin), azathioprine, mycophenolate mofetil); angiogenicagents: vascular endothelial growth factor (VEGF), fibroblast growthfactor (FGF); angiotensin receptor blockers; nitric oxide donors;anti-sense oligionucleotides and combinations thereof; cell cycleinhibitors, mTOR inhibitors, and growth factor receptor signaltransduction kinase inhibitors; retenoids; cyclin/CDK inhibitors; HMGco-enzyme reductase inhibitors (statins); and protease inhibitors.

As used herein, the singular form of “a,” “an,” and “the” include theplural referents unless specifically defined as only one. While thepresent invention has been disclosed with reference to certain preferredembodiments, numerous modifications, alterations, and changes to thedescribed embodiments are possible without departing from the sphere andscope of the present invention, as defined in the appended claims.Moreover, where methods, processes and steps described above indicatethat certain events occurring in certain order, those skilled in the artwould recognize that the ordering of steps may be modified and that suchmodifications are within the variations of the described embodiments.Accordingly, it is intended that the present invention not be limited tothe described embodiments, but that it have the full scope defined bythe language of the following claims, and equivalents thereof.

1. A stent device comprising: a stent frame, the stent frame having acentral axis, a luminal surface, and an abluminal surface, the stentframe having at least one gap along the abluminal surface providingcommunication between the abluminal and luminal surfaces, the at leastone gap defining a gap length; and a generally tubular graft membercontiguous with at least one of the luminal and abluminal surfaces ofthe stent frame, the graft member including an expansion portion to spanthe at least one gap, the expansion portion having a length greater thanthe gap length.
 2. The stent graft of claim 1, wherein the expansionportion has a length substantially equal to an arc length defined by thestent frame having a radius of curvature of about 20 mm.
 3. The stentgraft of claim 1, wherein the stent frame has a first state such thatthe gap length is at a minimum and a second state such that the gaplength is at a maximum.
 4. The stent graft of claim 3, wherein stentframe defines a center point of curvature such that the abluminalsurface includes an outer curved surface and inner curved surfacerelative to the center, the outer curved surface being in the secondstate and the inner surface being in the first state.
 5. The stent graftdevice of claim 1, wherein the stent frame has a first state and whereinthe stent frame is substantially straight and the stent frame has asecond state wherein the stent frame defines a radius of curvature ofabout 20 millimeters, and wherein the expansion portion is configured toaxially expand the tubular graft member as the stent frame goes from thefirst state to the second state.
 6. A method of making a stent-graftdevice comprising: tensioning a stent frame having an abluminal surfaceand a luminal surface to alter an initial aspect ratio of the stentframe and define a second aspect ratio; coupling a tubular graft memberto the stent frame; and relaxing the stent frame so as to contract thegraft member along the central axis.
 7. The method of claim 6, furthercomprising positioning the tubular graft member coaxially inside thestent.
 8. The method of claim 6, further comprising securing the tubulargraft member to the luminal surface.
 9. The method of claim 6, furthercomprising disposing the tubular graft member over a mandrel andsecuring a first and second end of the tubular graft member about themandrel.
 10. The method of claim 6, wherein tensioning the stent frameprovides axially elongating the frame such that the frame is elongatedan amount less than 20 percent of its original length.
 11. The method ofclaim 6, wherein relaxing the stent frame contracts the stent frame to alength that is about one hundred ten (110%) to about one-hundred fifteenpercent (110%-115%) its original length.
 12. The method of claim 6,wherein coupling the tubular graft member to the stent graft comprisescoupling the tubular member to the abluminal surface.
 13. The method ofclaim 12, wherein coupling the tubular graft member to the abluminalsurface includes applying a wrapping process to the tubular graft memberso that the tubular graft member bonds with an interior graft memberdisposed on the luminal surface.
 14. The method of claim 6, wherein thegraft member is secured to the stent frame on the basis of anintervening polymeric bonding layer.
 15. The method of claim 14, whereinthe polymeric bonding layer comprises a powder coating of, for instance,PTFE or PET applied to the stent frame.
 16. The method of claim 6,wherein relaxing the stent frame provides for an expansion length thatis about five to ten percent of the contracted length of the stent graftdevice.
 17. A stent device comprising: a first graft member; a secondgraft member; and a stent frame defining a central axis, the framehaving an abluminal surface engaged with the first graft member and aluminal surface engaged with the second graft member such that the firstgraft member and the second graft member encapsulates the stent framealong the length of the central axis, the stent frame including aconfiguration where the stent frame is disposed on a curvature such thatthe abluminal surface has a radius of curvature of approximately 20millimeters about a center of the curvature and the luminal surfacedefines a substantially constant effective cross-sectional area at anyportion generally transverse to the central axis of the stent framedisposed about the curvature.
 18. The stent device of claim 17, whereinthe second graft member is bonded to the first graft member.
 19. Thestent device of claim 17, wherein the first graft member defines anouter curved surface and an inner curved surface relative to the centerof curvature, the outer curved surface and the inner curved surfacebeing generally equidistant from the central axis.
 20. The stent deviceof claim 17, wherein the stent frame includes a substantially straightportion continuous with the curvature, the substantially straightportion defining an effective cross-sectional area substantially equalto an effective cross-sectional area proximate the curvature.
 21. Thestent device of claim 17, wherein the curvature of the stent frameincludes a gap proximate the apex of the curvature, the gap having a gaplength, the first graft member having an expansion portion configured tospan the gap, the expansion portion defining a radius of curvaturesubstantially equal to about 20 millimeters.
 22. The stent device ofclaim 17, wherein the radius of curvature ranges from about 30millimeters to about 10 millimeters.
 23. A stent device comprising: astent frame, the stent frame having a first end and a second enddefining a central axis therebetween; and a tubular graft memberconcentrically bound with the stent frame, the graft member including atleast one undulation between the first and second ends, the tubulargraft member being configured to extend along the central axis.
 24. Thestent device of claim 23, wherein the stent frame defines a radius ofcurvature such that the tubular graft member forms an outer curvedsurface and an inner curved surface, wherein the at least one undulationis located along the inner curved surface.
 25. The stent device of claim23, wherein the stent frame has a first state wherein the stent frame issubstantially straight such that the at least one undulation is disposedproximate a gap in the stent frame, and a second state wherein the stentframe defines a radius of curvature expanding the gap so as to eliminatethe undulation.
 26. The stent device of claim 23, wherein the tubulargraft member is coaxially positioned inside the stent frame.
 27. Thestent device of claim 23, wherein the tubular graft member is secured tothe stent frame on the basis of an intervening polymeric bonding layer.28. The stent device of claim 27, wherein the polymeric bonding layercomprises a powder coating of, for instance, PTFE or PET applied to thestent frame.
 29. The stent device of claim 23, wherein the tubular graftmember comprises an inner tubular graft member and an outer tubulargraft member which are bonded to each other through openings in thestent frame.